The Paypal Resolution Centre is at the top of your PP account page under Tools.
The first step suggested is to Contact the Seller.
This is polite but not necessary.
If you decide to just ask When was this shipped? What service was used? What is the tracking number?
Don't worry if there is no tracking. This is an expensive service and in any case is used only as a Seller Protection.
What you want is a refund.
Do NOT accept an offer of a replacement. It won't arrive either.
If you don't get an immediate refund (or if the seller offers the bogus replacement) ask PP to step in and escalate to a Claim.
If the seller cannot prove Delivery (not shipping, delivery) you will be refunded.